The invention relates to a filter for filtering human blood, especially in an extracorporeal circulatory system. In a known blood filter of this type (DE-PS No. 21 55 820) the filter is designed in an essentially dynamically balanced manner, whereby blood inlet and blood outlet are located in the axis of rotation of the housing. A gas outlet valve is provided at the highest point of the blood outlet chamber, that is, on the arterial side of the filter element. The filter element itself is designed as a hollow, cylindrical filter member whose front surfaces are each enclosed by an end cap in a sealing manner, whereby the upper end cap closes the hollow cylindrical space in the extension of the blood inlet so that the blood flows from the inner cylinder space through the filter member into the outer cylinder space.
The filter element has the task of filtering microemboli out of the blood and the gas outlet valve on the patient side of the filter element has the task of discharging gas bubbles which collect at the highest point of the cylinder housing to the outside in order to avoid gas emboli.
Such filters are operated in a vertical position in conjunction with a heart-lung machine, whereby it is located in a customary arrangement of the filter over the heart-lung machine and the outlet of the blood filter on the patient side is located approximately at the level of the patient.
The known filter according to the generic part of the main claim is in need of improvement in as far as the blood outlet of the filter on the patient side is vertically directed and bends of the connection hose located on the filter outlet and running laterally to the patient frequently occur.
Filters are also known in which both connections project axially downward so that similar problems occur here too and the connections conceal an additional safety risk. Another safety risk in the known filters is the fact that the blood transported out of the heart-lung machine does not have sufficient opportunity to become quiescent within the filter housing so that this increases the danger of gas emboli.
Such filter are frequently employed in open heart operations and on other organs, as is described in DE-PS No. 32 04 317 and in the article "Myocardial `Equilibration Processes` and Myocardial Energy Turnover during Initiation of Articificial Cardiac Arrest with Cardioplegic Solution-Reasons for a Sufficiently Long Cardioplegic Perfusion" published in "Thorac. Cardiovasc. Surgeon" 29, 1981, pp. 71-6. In such operations the blood or a cardioplegic solution is cooled down to approximately +4.degree. to +6.degree. C. in the heart-lung machine. The design of the known filters does not offer any possibility of detecting by measuring techniques the development of air bubles in the fluid to be filtered and the temperature of the liquid in the filter. This is only possible in the individual line sections outside of the filter.
The known filters (EP-OS No. 82 721=U.S. Ser. No. 333,832, U.S. Pat. No. 3,701,433) are usually constructed of transparent plastic in four and more parts. In spite of the transparency, on account of the housing construction and the arrangement of the filter element within this construction, only either the one or the other chamber side of the housing can be observed for the formation of gas bubbles and vented. In order to remove the enclosed gas during the filling of the filter, it is made possible for the enclosed gas in the non-ventable chamber to escape into the ventable chamber by rotating the filter by 180.degree.. This procedure must usually be performed several times, is unsatisfactory as concerns manipulation and is not without risk from a medical point of view.
The invention therefore has the task of improving with simple means a filter as concerns its manipulation during venting and its operational safety as regards the dangers inherent in the formation of gas bubbles and in the bending of the connection hose to the patient without increasing the number of its individual parts, which would increase the expense.